Cell selection method and mobile station

ABSTRACT

A cell selection method includes steps of: (A) determining, at a mobile station (UE), whether or not a first CSG cell satisfies a predetermined condition, when using a first macro cell as a camped cell; and (B) changing, at the mobile station (UE), the camped cell from the first macro cell to a first CSG cell, when determined that the first CSG cell satisfies the predetermined condition.

TECHNICAL FIELD

The present invention relates to a cell selection method in which amobile station selects a camped cell among specific cells selectable asa camped cell only by a specific mobile station and general cellsselectable as a camped cell by any mobile station. The present inventionalso relates to the mobile station.

BACKGROUND ART

There is a discussion in the 3GPP (3rd Generation Partnership Project)RAN-WG on a home base station HNB employing the “LTE (Long TermEvolution)” as a radio access scheme.

Specifically, in the current 3GPP specifications, a mobile communicationsystem is configured to manage a specific mobile station (a mobilestation permitted to select a specific cell as a camped cell) belongingto a CSG (Closed Subscriber Group) under control of the home basestation HNB.

In other words, in the current 3GPP specifications, only a specificmobile station belonging to a CSG can perform communication via a CSGcell (specific cell) under control of the home base station HNB.

However, the current 3GPP specifications do not define a method in whichthe mobile station selects a camped cell in an environment where CSGcells and macro cells coexist.

Accordingly, the following situation may occur. Specifically, even whena mobile station using a macro cell as a camped cell enters an areawhere a CSG cell regarding the mobile station as a specific mobilestation is selectable as a camped cell, the mobile station cannot detectthat, and thus cannot change the camped cell to the CSG cell.

The present invention has been made in consideration of the aboveproblem, and has an objective to provide a cell selection method and amobile station that allow a camped cell to be properly selected in anenvironment where CSG cells and macro cells coexist.

DISCLOSURE OF THE INVENTION

A first aspect of the present invention is summarized as a cellselection method in which a mobile station selects a camped cell among aspecific cell selectable as a camped cell only by a specific mobilestation and a general cell selectable as a camped cell by any mobilestation, the cell selection method including steps of: (A) determining,at the mobile station, whether or not a predetermined condition issatisfied, when using a first general cell as the camped cell; and (B)changing, at the mobile station, the camped cell from the first generalcell to a first specific cell, when determined that the predeterminedcondition is satisfied.

In the first aspect, in the step (A), the mobile station can determinewhether or not the predetermined condition is satisfied, when using thefirst general cell as the camped cell, and when determined that themobile station is located in the general cell which at least partiallyoverlaps the first specific cell that regards the mobile station as thespecific mobile station.

In the first aspect, a first frequency used by the first specific cellcan be different from a second frequency used by the first general cell;and when determined that the first specific cell has best radio qualityamong cells using the first frequency, and when determined that theradio quality in the first specific cell satisfies first radio quality,the mobile station can determine that the predetermined condition issatisfied, in the step (A), and can change the camped cell from thefirst general cell to the first specific cell, in the step (B).

In the first aspect, a first frequency used by the first specific cellcan be different from a second frequency used by the first general cell;and when determined that a difference between radio quality in the firstspecific cell and best radio quality among cells using the firstfrequency is within a predetermined offset, and determined that theradio quality in the first specific cell satisfies first radio quality,the mobile station can determine that the predetermined condition issatisfied, in the step (A), and can change the camped cell from thefirst general cell to the first specific cell, in the step (B).

In the first aspect, when determined that radio quality in the firstspecific cell satisfies first radio quality, the mobile station candetermine that the predetermined condition is satisfied, in the step(A), and can change the camped cell from the first general cell to thefirst specific cell, in the step (B).

In the first aspect, the cell selection method can further include astep of (C) setting, at the mobile station, a second specific cell asthe camped cell, when not detected a general cell that satisfies secondradio quality, and when detected the second specific cell that does notregard the mobile station as the specific mobile station and satisfiesthird radio quality.

In the first aspect, the cell selection method can further include astep of: changing, at the mobile station, the camped cell from thesecond specific cell to a second general cell, when using the secondspecific cell as the camped cell, and when detected a second generalcell that satisfies the second radio quality.

A second aspect of the present invention is summarized as a mobilestation configured to select a camped cell among a specific cellselectable as a camped cell only by a specific mobile station and ageneral cell selectable as a camped cell by any mobile station, themobile station including: a cell selector unit configured to determinewhether or not a predetermined condition is satisfied when using a firstgeneral cell as a camped cell, and to change the camped cell from thefirst general cell to a first specific cell when determined that thepredetermined condition is satisfied.

In the second aspect, the cell selector unit can be configured todetermine whether or not the predetermined condition is satisfied, whenusing the first general cell as the camped cell, and when determinedthat the mobile station is located in the general cell which at leastpartially overlaps the first specific cell that regards the mobilestation as the specific mobile station.

In the second aspect, a first frequency used by the first specific cellcan be different from a second frequency used by the first general cell;and when determined that the first specific cell has best radio qualityamong cells using the first frequency, and that the radio quality in thefirst specific cell satisfies first radio quality, the cell selectorunit can be configured to determine that the predetermined condition issatisfied, and to change the camped cell from the first general cell tothe first specific cell.

In the second aspect, a first frequency used by the first specific cellcan be different from a second frequency used by the first general cell;and when determined that a difference between radio quality in the firstspecific cell and best radio quality among cells using the firstfrequency is within a predetermined offset, and determined that theradio quality in the first specific cell satisfies first radio quality,the cell selector unit can be configured to determine that thepredetermined condition is satisfied, and to change the camped cell fromthe first general cell to the first specific cell.

In the second aspect, when determined that radio quality in the firstspecific cell satisfies first radio quality, the cell selector unit canbe configured to determine that the predetermined condition issatisfied, and to change the camped cell from the first general cell tothe first specific cell.

In the second aspect, when not detected a general cell that satisfiessecond radio quality, and when detected a second specific cell that doesnot regard the mobile station as the specific mobile station andsatisfies third radio quality, the cell selector unit can be configuredto set the second specific cell as the camped cell.

In the second aspect, when using the second specific cell as the campedcell, and when detected a second general cell that satisfies the secondradio quality, the cell selector unit can be configured to change thecamped cell from the second specific cell to the second general cell.

A third aspect of the present invention is summarized as a cellselection method in which a mobile station selects a camped cell among afirst cell using a first frequency and a second cell using a secondfrequency different from the first frequency, the cell selection methodincluding a step of: changing, at the mobile station which uses thefirst cell as the camped cell, the camped cell from the first cell tothe second cell, when a priority level of the second cell is higher thana priority level of the first cell, and when determined that radioquality in the second cell satisfies predetermined radio quality.

A fourth aspect of the present invention is summarized as a cellselection method in which a mobile station selects a camped cell among afirst cell using a first frequency and a second cell using a secondfrequency different from the first frequency, the cell selection methodincluding a step of: changing, at the mobile station which uses thefirst cell as the camped cell, the camped cell from the first cell tothe second cell, when a priority level of the second cell is the same asa priority level of the first cell, and when determined that radioquality in the second cell satisfies predetermined radio quality andthat radio quality in the first cell does not satisfy predeterminedradio quality.

A fifth aspect of the present invention is summarized as a cellselection method in which a mobile station selects a camped cell among afirst cell using a first frequency and a second cell using a secondfrequency different from the first frequency, the cell selection methodincluding a step of: changing, at the mobile station which uses thefirst cell as the camped cell, the camped cell from the first cell tothe second cell, when a priority level of the second cell is lower thana priority level of the first cell, and when determined that radioquality in the second cell satisfies predetermined radio quality andthat radio quality in the first cell does not satisfy predeterminedradio quality.

In the third to fifth aspects, the mobile station can change the campedcell from the first cell to the second cell, when the second cell is aspecific cell selectable as a camped cell only by a specific mobilestation, and when determined that a difference between radio quality inthe second cell and best radio quality among cells using the secondfrequency is within a predetermined offset.

A sixth aspect of the present invention is summarized as a mobilestation configured to select a camped cell among a first cell using afirst frequency and a second cell using a second frequency differentfrom the first frequency, the mobile station including: a cell selectorunit configured to change the camped cell from the first cell to thesecond cell, when a priority level of the second cell is higher than apriority level of the first cell, when the first cell is used as thecamped cell, and when determined that radio quality in the second cellsatisfies predetermined radio quality.

A seventh aspect of the present invention is summarized as a mobilestation configured to select a camped cell among a first cell using afirst frequency and a second cell using a second frequency differentfrom the first frequency, the mobile station including: a cell selectorunit configured to change the camped cell from the first cell to thesecond cell, when a priority level of the second cell is the same as apriority level of the first cell, when the first cell is used as thecamped cell, and when determined that radio quality in the second cellsatisfies predetermined radio quality and that radio quality in thefirst cell does not meet predetermined radio quality.

A eighth aspect of the present invention is summarized as a mobilestation configured to select a camped cell among a first cell using afirst frequency and a second cell using a second frequency differentfrom the first frequency, the mobile station including: a cell selectorunit configured to change the camped cell from the first cell to thesecond cell, when a priority level of the second cell is lower than apriority level of the first cell, when the first cell is used as thecamped cell, and when determined that radio quality in the second cellsatisfies predetermined radio quality and that radio quality in thefirst cell does not meet predetermined radio quality.

In the sixth to eighth aspects, the cell selector unit can be configuredto change the camped cell from the first cell to the second cell, whenthe second cell is a specific cell selectable as a camped cell only by aspecific mobile station, and when determined that a difference betweenradio quality in the second cell and best radio quality among cellsusing the second frequency is within a predetermined offset.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the overall configuration a mobilecommunication system according to a first embodiment of the presentinvention.

FIG. 2 is a functional block diagram of a mobile station according tothe first embodiment of the present invention.

FIG. 3 is a diagram illustrating an operation of determining a campedcell of the mobile station, according to the first embodiment of thepresent invention.

FIG. 4 is a flowchart showing an operation of determining a camped cellof the mobile station, according to the first embodiment of the presentinvention.

FIG. 5 is a flowchart showing an operation of determining a camped cellof the mobile station, according to the first embodiment of the presentinvention.

FIG. 6 is a flowchart showing an operation of determining a camped cellof the mobile station, according to the first embodiment of the presentinvention.

FIG. 7 is a diagram illustrating a mobile communication system accordingto Modification 1 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Configuration of a MobileCommunication System According to a First Embodiment of the PresentInvention

Referring to FIGS. 1 to 3, the configuration of a mobile communicationsystem according to a first embodiment of the present invention will bedescribed.

As FIG. 1 shows, the mobile communication system according to theembodiment includes: a switching apparatus MME (Mobility ManagementEntity); home base stations HNB #1 and #2 that manage CSG cells(specific cells) #1 and #2, respectively; radio base stations eNB #1 and#2 that manage macro cells (general cells) #1 and #2, respectively; anda mobile station UE.

Here, the CSG cell is a cell for which a CSG is set up, whereas themacro cell is a cell for which no CSG is set up. The CSG is a grouphaving an access right to a set-up CSG cell.

When not belonging to a CSG set up for a certain CSG cell, the mobilestation UE is a “general mobile station” in that certain CSG cell. Whenbelonging to a CSG set up for a certain CSG cell, on the other hand, themobile station UE is a “specific mobile station” in that certain CSGcell.

In the mobile communication system according to the embodiment, the CSGcell #1 regards the mobile station UE as a “specific mobile station” (amobile station permitted to use the CSG cell #1 as a camped cell,namely, a mobile station permitted to perform communication via the CSGcell #1). On the other hand, the CSG cell #2 does not regard the mobilestation UE as a “specific mobile station”. Accordingly, to the mobilestation UE, the CSG cell #1 is an “own CSG cell”, and the CSG cell #2 isan “other CSG cell”.

In addition, in the example shown in FIG. 1, the CSG cell #1 partiallyoverlaps the macro cells #1 and #2, and the CSG cell #2 also partiallyoverlaps the macro cells #1 and #2.

Note that the CSG can be set up not only for a cell under control of aso-called home base station installed in houses, but also for a generalcell under control of a radio base station installed in officebuildings, cafes, schools, and elsewhere. For example, possiblesituations include giving an access right only to the employees of anoffice, or giving an access right temporarily to the employees andcustomers of a cafe.

In such cases, the same CSG may be set up for multiple cells or multipleradio base stations. The radio base stations are ranged from small-sizedlow-power ones to large-sized high-power ones.

Accordingly, in the description herein, the above scenarios areencompassed, and a radio base station managing a cell for which a CSG isset up (CSG cell) is specially called a “home base station HNB” forconvenience reasons.

The switching apparatus MME is configured to manage specific mobilestations in CSG cells under control of the home base stations HNBconnected to the switching apparatus MME (namely, configured to managespecific mobile stations permitted to perform communication via the CSGcells).

Alternatively, it may be the home base station HNB that is configured tomanage a specific mobile station in a cell under control of the homebase station HNB. However, the home base station HNB can be installedwhere the user can reach. Accordingly, considering factors such assecurity, it is preferable that the switching apparatus MME beconfigured to manage specific mobile stations in CSG cells as describedabove.

As FIG. 2 shows, the mobile station UE has a broadcast informationreceiver unit 11, an individual signal receiver unit 12, a parameterstorage unit 13, a cell information manager unit 14, a search locationinformation manager unit 15, and a cell selector unit 16.

The broadcast information receiver unit 11 is configured to receivebroadcast information transmitted via a BCH (Broadcast Channel), an SU(Scheduling Unit) or the like, from the radio base station eNB or thehome base station HNB managing the camped cell (a CSG cell or a macrocell) of the mobile station UE.

For example, The broadcast information receiver unit 11 is configured toreceive, as the broadcast information, information identifying a cell(or a TA: Tracking Area) where the mobile station UE is currentlylocated (a cell ID and a TA-ID).

The broadcast information receiver unit 11 is configured to alsoreceive, as the broadcast information, information on the frequency of acell that at least partially overlaps the cell (a CSG cell or a macrocell) where the mobile station UE is currently located(different-frequency information).

Here, in a case where the mobile station UE is located in a cell. F2having a frequency f2, the broadcast information receiver unit 11 isconfigured to receive, as the “different-frequency information”,information (a TA-ID and a cell ID) identifying each of cells F1, F3,and F4 that overlaps the cell F2 at least partially; frequencies f1, f3,and f4 (e.g., xxMHz) used by the respective cells F1, F3, and F4overlapping the cell F2 at least partially; and the like.

The individual signal receiver unit 12 is configured to receive anindividual signal transmitted from the switching apparatus MME.

For example, the individual signal receiver unit 12 is configured toreceive, as the individual signal, a “list of own CSG cells,” a “list ofoverlapping macro cells” and the like. The “list of own CSG cells” listsCSG cells for which the CSG to which the mobile station OE belongs isset up. For each of the own CSG cells, the “list of overlapping macrocells” lists macro cells that overlap the CSG cell at least partially.

Here, the individual signal receiver unit 12 may be configured toreceive, as the individual signal, the above-described “list of own CSGcells”, “list of overlapping macro cells” and the like, upon entrance toa macro cell (or a TA) overlapping an own CSG cell of the mobile stationUE at least partially.

The parameter storage unit 13 is configured to store parameters, such as“Hysteresis (e.g., xx dB)”, “Treselection (e.g., xx seconds)” and“Margin (e.g., xx dB)” included in determination information used fordetermining whether or not to change the camped cell of the mobilestation UE.

Each of these parameters may be a different value for each cell, or be acommon value for multiple cells. In addition, these parameters may benotified of as the aforementioned broadcast information or as theaforementioned individual signal.

The cell information manager unit 14 is configured to manage informationon each cell (cell information).

The cell information manager unit 14 is configured to manage, as thecell information, a “priority level”, a threshold “QRSRPmin” or“QRSRQmin”, a “frequency used”, a predetermined offset “OffsetRSRP” or“Of fsetRSRQ” and the like, for each cell.

Note that the threshold “QRSRPmin” or “QRSRQmin” and the predeterminedoffset “OffsetRSRP” or “OffsetRSRQ” may be a different value for eachcell, or be a common value for multiple cells.

Moreover, the threshold “QRSRPmin” and “QRSRQmin” may be called“ThreshServing, low”, “ThreshX, low”, “ThreshX, high” and the like.

Each information element included in the cell information may benotified of as the aforementioned broadcast information or as theaforementioned individual signal.

In the example shown in FIG. 3, the “own CSG cells” of the mobilestation UE each have a “high” priority level; “macro cells” each have an“intermediate” priority level; and the “other CSG cells” of the mobilestation UE each have a “low” priority level. Note that the carrierfrequency of the “own CSG cells” and the carrier frequency of the “otherCSG cells” may be different or the same.

The search location information manager unit 15 is configured to managesearch location information defining a location where the mobile stationUE should start searching for the own CSG cell.

For example, the search location information manager unit 14 may beconfigured to directly manage, as the search location information, the“list of own CSG cells” and the “list of overlapping macro cells”received by the individual signal receiver unit 12. In this case, the“search location” is the macro cells included in the “list ofoverlapping macro cells”.

Alternatively, the search location information manager unit 15 may beconfigured to manage search location information (Finger Print) uniquelygenerated based on the “list of own CSG cells” and the “list ofoverlapping macro cells” received by the individual signal receiver unit12. In this case, the “search location” is a location defined by “GPSinformation” or the like.

Furthermore, the search location information manager unit 15 may beconfigured to manage search location information generated based on thepropagation levels or the like of cells included in the “list ofoverlapping macro cells”.

The cell selector unit 16 is configured to select a camped cell (a cellwhere the mobile station LTE should camp on) among CSG cells (specificcells selectable as a camped cell only by specific mobile stations) andmacro cells (general cells selectable as a camped cell by any mobilestations).

As FIG. 3 shows, the cell selector unit 16 is configured to select thecamped cell based on the priority level of each cell.

In the example shown in FIG. 3, regarding to the mobile station UE,cells #1-1 and #1-2 (own CSG cells) using the frequency f1 each have a“high” priority level; cells #2-1, #2-2, #3-1, and #3-2 (macro cells)using either the frequency f2 or the frequency f3 each have an“intermediate” priority level; and cells #4-1 and #4-2 (other CSG cells)using the frequency f4 each have a “low” priority level. Note that thefrequencies f1 and f4 may be different frequencies, or be the samefrequency.

Here, the cell selector unit 16 is configured to perform a search, at apredetermined interval “TEqual”, whether or not there is any cellselectable as a camped cell for the mobile station UE among the cellshaving the same priority level as the current camped cell of the mobilestation UE.

Note that the cell selector unit 16 may be configured not to perform thesearch, when the radio quality “Serving (RSRQ (Reference Signal ReceivedQuality) or RSRP (Reference Signal Received Power))” in the currentcamped cell of the mobile station UE is a threshold “SSerchEqual” ormore.

For example, as FIG. 3 shows, when using the “cell #1-1” which uses thefrequency f1 and has a “high” priority level, as the camped cell, andwhen a predetermined condition A (R-criteria) is satisfied, the cellselector unit 16 is configured to change the camped cell from the “cell#1-1” to the “cell #1-2” using the frequency f1 and having a “high”priority level.

In addition, as FIG. 3 shows, when using the “cell #2-1” which uses thefrequency f2 and has an “intermediate” priority level, as the campedcell, and when the predetermined condition A is satisfied, the cellselector unit 16 is configured to change the camped cell from the “cell#2-1” to either the “cell #2-2” using the frequency f2 and having an“intermediate” priority level or the “cell #3-1” using the frequency f3and having an “intermediate” priority level (see the operation shown inFIG. 5 described later).

Moreover, as FIG. 3 shows, when using the “cell #4-1” which uses thefrequency f4 and has a “low” priority level, as the camped cell, andwhen the predetermined condition A is satisfied, the cell selector 16 isconfigured to change the camped cell from the “cell #4-1” to the “cell#4-2” using the frequency f4 and having a “low” priority level.

Here, the cell selector unit 16 is configured to determine that thepredetermined condition A is satisfied when the following Equation (1)holds true.

“Neighbour”+“OffsetRSRP (or OffsetRSRQ)”>“Serving”+“Hysteresis”  Equation (1)

Here, “Neighbour” is the radio quality in a cell adjacent to the currentcamped cell of the mobile station UE (the “cell #1-2”, the “cell #2-2”,the “cell #3-1” or the “cell #4-2”) ; “OffsetRSRP (or Offset RSRQ) is apredetermined offset; “Serving” is the radio quality in the currentcamped cell of the mobile station UE (the “cell #1-1”, the “cell #2-1”or the “cell #4-1”); and “Hysteresis” is a predetermined parameter.

Meanwhile, as FIG. 3 shows, when using the “cell #1-2” as the campedcell, and when a predetermined condition B is satisfied, for example,the cell selector unit 16 is configured to change the camped cell fromthe “cell #1-2” to the “cell #2-2”.

Moreover, when using the “cell #3-2” as the camped cell, and when thepredetermined condition B is satisfied, the cell selector unit 16 isconfigured to change the camped cell from the “cell #3-2” to the “cell#4-2” (see the operation shown in FIG. 6 described later).

Here, the cell selector unit 16 is configured to determine that thepredetermined condition B is satisfied, when not detected a cell thatsatisfies second communication quality (namely, a cell in which (radioquality “RSRP” or “RSRQ”)<(“QRSRPmin” or “QRSRQmin”)+(parameter“Margin”) holds true) among the cells having the same priority level asthe current camped cell of the mobile station UE; and when detected acell that has a lower priority level than the current camped cell of themobile station UE and satisfies third radio quality (namely, a cell inwhich (radio quality “RSRP” or “RSRQ”)>(“QRSRPmin” or“QRSRQmin”)+(parameter “Hysteresis”) holds true).

Here, the cell selector unit 16 is configured to perform a search, at apredetermined interval “THigher”, whether or not there is any cellselectable as a camped cell for the mobile station UE among the cellshaving a higher priority level than the current camped cell of themobile station UE.

Here, the mobile station UE may be notified of the predeterminedintervals “TEqual” and “THigher” through the broadcast information andthe individual signal described above. Note that the predeterminedintervals “TEqual” and “THigher” may be the same interval or bedifferent intervals.

For example, as FIG. 3 shows, when using the “cell #4-1” as the campedcell, and when a predetermined condition C is satisfied, the cellselector unit 16 is configured to change the camped cell from the “cell#4-1” to the “cell #3-1”.

Moreover, as FIG. 3 shows, the cell selector unit 16 is configured tochange the camped cell from the “cell #2-1” to the “cell #1-1”, whenusing the “cell #2-1” as the camped cell; when the mobile station UE isdetermined as being located in the “cell #2-1 (a general cell)” that atleast partially overlaps the “cell #1-1 (a first specific cell thatregards the mobile station UE as a “specific mobile station”)”; and whenthe predetermined condition C is satisfied (see the operation shown inFIG. 4 described later).

Here, the cell selector unit 16 may be configured to determine that thepredetermined condition C is satisfied, when determining that the “cell#1-1 (the first specific cell) has the best “RSRP or RSRQ (radioquality)” among the cells using the frequency f1 (first frequency); andwhen determining that the “RSRP or RSRQ (radio quality)” of the “cell#1-1 (first specific cell)” satisfies first radio quality (namely, when(radio quality “RSRP” or “RSRQ”)>(“QRSRPmin” or “QRSRQmin”) holds true).

Alternatively, the cell selector unit 16 may be configured to determinethat the predetermined condition C is satisfied, when determining thatthe difference between the “RSRP or RSRQ (radio quality)” of the “cell#1-1 (first specific cell)” and the best “RSRP or RSRQ (radio quality)”among the cells using the frequency f1 (first frequency) is within thepredetermined offset “OffsetRSRP or OffsetRSRQ; and when determiningthat the “RSRP or RSRQ (radio quality)” of the “cell #1-1 (firstspecific cell)” satisfies the first radio quality (namely, when (radioquality “RSRP” or “RSRQ”)>(“QRSRPmin” or “QRSRQmin”) holds true).

Still alternatively, the cell selector unit 16 may be configured todetermine that the predetermined condition C is satisfied, whendetermining that the “RSRP or RSRQ (radio quality)” of the “cell #1-1(first specific cell)” satisfies the first radio quality (namely, when(radio quality “RSRP” or “RSRQ”)>(“QRSRPmin” or “QRSRQmin”) holds true).

Operation of the Mobile Communication System According to the FirstEmbodiment of the Present Invention

Referring to FIGS. 4 to 6, an operation of the mobile communicationsystem according to the first embodiment of the present invention willbe described.

First, with reference to FIG. 4, a description will be given of anoperation in which the mobile station UE changes a camped cell from a“macro cell” to an “own CSG cell”.

As FIG. 4 shows, in Step S101, upon receipt of the “list of own CSGcells” and the “list of overlapping macro cells” from the switchingapparatus MME, the mobile station UE determines whether or not the“information identifying a macro cell (a TA-ID and a cell ID)” havingbeen notified of through the broadcast information is in the “list ofoverlapping macro cells” included in the individual signal received fromthe switching apparatus MME. Thereby, the mobile station UE determineswhether or not the mobile station UE is located in the macro cell whichoverlaps an own CSG cell at least partially.

Alternatively, in Step S101, the mobile station UE determines whether ornot the mobile station UE is located within a “search location” byreferring to the search location information manager unit 15. Thereby,the mobile station UE determines whether or not the mobile station UE islocated in the macro cell which overlaps an own CSG cell at leastpartially.

When determined as being located in such a macro cell, the mobilestation UE repeats the processing in Step S101.

When determined as being located in such a macro cell, and when detecteda lapse of the predetermined period “THigher” in Step S102, the mobilestation UE determines whether or not there is an own CSG cell satisfyingthe predetermined condition C.

When determined that there is an own CSG cell satisfying a predeterminedcondition D, in Step S104, the mobile station UE changes the camped cellto the own CSG cell satisfying the predetermined condition C.

On the other hand, when the mobile station UE determines that there isno own CSG cell satisfying the predetermined condition C, the operationreturns to Step S101.

Second, with reference to FIG. 5, a description will be given of anoperation in which the mobile station UE changes a camped cell from a“first macro cell” to a “second macro cell”.

As FIG. 5 shows, when detected a lapse of the predetermined period“TEqual” in Step S201, the mobile station in determines whether or notthe radio quality “Serving (RSRP or RSRQ)” is larger than the threshold“SSearchEqual” in Step S202.

When the determination result in Step S202 is negative (NO), theoperation returns to Step S201.

On the other hand, when the determination result in Step S202 isaffirmative (YES), the mobile station UE determines whether or not thefollowing Equation (2) holds true in Step S203.

(“Neighbour (RSRP or RSRQ)” being the radio quality in the second macrocell adjacent to the first macro cell)+(predetermined offset“OffsetRSRP” or “OffsetRSRQ”)>(“Serving (RSRP or RSRQ)” being the radioquality in the first macro cell)+(parameter “Hysteresis”)   Equation (2)

When the determination result in Step S203 is negative (NO), theoperation returns to Step S201.

On the other hand, when the determination result in Step S203 isaffirmative (YES), the mobile station UE changes the camped cell fromthe “first macro cell” to the “second macro cell”.

Third, with reference to FIG. 6, a description will be given of anoperation in which the mobile station UE changes a camped cell from a“macro cell” to an “other CSG cell”.

In Step S301, the mobile station UE determines whether or not the mobilestation UE detects a cell in which (radio quality “RSRP” or“RSRQ”)<(QRSRPmin” or “QRSRQmin”) (parameter “Margin”) holds true.

When the determination result in Step S301 is negative (NO), theoperation returns to Step S301.

On the other hand, when the determination result in Step S301 isaffirmative (YES), the mobile station UE determines whether or not themobile station 11E detects a cell in which (radio quality “RSRP” or“RSRQ”)>(“QRSRPmin” or “QRSRQmin”)+(parameter “Hysteresis”) holds truein Step 302.

When the determination result in Step S302 is negative (NO), the mobilestation UE detects as being out of area in Step S304.

On the other hand, when the determination result in Step S302 isaffirmative (YES), the mobile station UE selects the cell (other CSGcell) detected in Step S302 as the camped cell, in Step S303.

Advantageous Effects of the Mobile Communication System According to theFirst Embodiment of the Present Invention

With the mobile communication system according to the embodiment, acamped cell can be selected properly in an environment where CSG cellsand macro cells coexist.

Modification 1

Referring to FIG. 7, a mobile communication system according toModification 1 will be described, focusing on differences from themobile communication system according to the first embodiment describedabove.

In the example shown in FIG. 7, regarding to the mobile station UE, acell #11 using a frequency f11 and a cell #12 using a frequency f12 eachhave a “high” priority level; a cell #21 using a frequency f21 and acell #22 using a frequency f22 each have an “intermediate” prioritylevel; and a cell #31 using a frequency f31 and a cell #32 using afrequency f32 each have a “low” priority level. Note that the cells #11,#12, #21, #22, #31, and #32 may be a macro cell or be a CSG cell. Inaddition, the frequencies f11, f12, f21, f22, f31, and f32 are differentfrequencies.

For example, as FIG. 7 shows, when using the “cell #11” as the campedcell, and when a predetermined condition Al is satisfied, the cellselector unit 16 is configured to change the camped cell from the “cell#11” to the “cell #12”.

Moreover, as FIG. 7 shows, when using the “cell #21” as the camped cell,and when the predetermined condition A1 is satisfied, the cell selectorunit 16 is configured to change the camped cell from the “cell #21” tothe “cell #22”.

Moreover, as FIG. 7 shows, when using the “cell #31” as the camped cell,and when the predetermined condition A1 is satisfied, the cell selectorunit 16 is configured to change the camped cell from the “cell #31” tothe “cell #32”.

Here, in a case where the “cell #12”, the “cell #22” or the “cell #32”is a macro cell, the cell selector unit 16 is configured to determinethat the predetermined condition A1 is satisfied, when the followingEquation (2) holds true, namely, when the radio quality in the “cell#12”, the “cell #22” or the “cell #32” satisfies predetermined radioquality and when the radio quality in the “cell #11”, the “cell #21” orthe “cell #31” does not meet predetermined radio quality.

“Neighbour”+“Offset 1”>“threshold 1”, and

“Serving”+“Offset 2”<“threshold 2”  Equation (2)

Here, “Neighbour” is the radio quality in a cell adjacent to the currentcamped cell of the mobile station UE (the “cell #12”, the “cell #22” orthe “cell #32”) ; and “Serving” is the radio quality in the currentcamped cell of the mobile station UE (the “cell #11”, the “cell #21” orthe “cell #31”).

Meanwhile, in a case where the “cell #12”, the “cell #22” or the “cell#32” is a CSG cell, the cell selector unit 16 is configured to determinethat the predetermined condition A1 is satisfied, when the followingEquation (3) holds true, namely, in addition to the conditions of theEquation (2) described above being satisfied, when the differencebetween the radio quality in the “cell #12”, the “cell #22” or the “cell#32” and the best radio quality among cells using any of the secondfrequencies f12, f22, and f32 is within a predetermined offset.

“Neighbour”+“Offset 1”>“threshold 1”, and

“Serving”+“Offset 2”<“threshold 2”, and

“Neighbour”>“R0”−“Offset 3”  Equation (3)

Here, “R0” is the radio quality in a cell having the best radio qualityamong cells using the same frequency as the frequency (f12, f22, or f32)used in a cell (the “cell #12”, the “cell #22” or the “cell #32”)adjacent to the current camped cell of the mobile station UE.

Furthermore, as FIG. 7 shows for example, when using the “cell #12” asthe camped cell, and when a predetermined condition B1 is satisfied, thecell selector unit 16 is configured to change the camped cell from the“cell #12” to the “cell #22”.

Moreover, when using the “cell #22” as the camped cell, and when thepredetermined condition B1 is satisfied, the cell selector unit 16 isconfigured to change the camped cell from the “cell #22” to the “cell#32”.

Here, the cell selector unit 16 is configured to determine that thepredetermined condition B1 is satisfied, when the “cell #22” or the“cell #32” is a macro cell, and when the following Equation (4) holdstrue, namely, when the radio quality in the “cell #22” or the “cell #32”satisfies predetermined radio quality and when the radio quality in the“cell #11” or the “cell #21” does not meet predetermined radio quality.

“Neighbour”+“Offset 4”>“threshold 3”, and

“Serving”+“Offset 5”<“threshold 4”  Equation (4)

Here, “Neighbour” is the radio quality in a cell adjacent to the currentcamped cell of the mobile station UE (the “cell #22” or the “cell #32”);and “Serving” is the radio quality in the current camped cell of themobile station UE (the “cell #12” or the “cell #22”).

In addition, the cell selector unit 16 may be configured to determinethat the predetermined condition B1 is satisfied, when the followingEquation (4-1) holds true, in addition to the Equation (4) describedabove holding true. Specifically, the Equation (4-1) holds true, whenthere is no cell that satisfies the predetermined radio quality amongthe cells using the same frequency as the frequency (f12 or f22) used inthe current camped cell (the “cell #12” or the “cell #22”) of the mobilestation UE.

“X”+“Offset 5”<“threshold 4”  Equation (4-1)

Here, “X” is the radio quality in each cell using the same frequency asthe frequency (f12 or f22) used in the current camped cell (the “cell#12” or the “cell #22”) of the mobile station UE.

On the other hand, the cell selector unit 16 is configured to determinethat the predetermined condition El is satisfied, when the “cell #22” orthe “cell #32” is a CSG cell, and when the following Equation (5) holdstrue, namely, in addition to the conditions of the Equation (4)described above being satisfied, when the difference between the radioquality in the “cell #22” or the “cell #32” and the best radio qualityamong cells using any of the second frequencies f22 and f32 is within apredetermined offset.

“Neighbour”+“Offset 4”>“threshold 3”, and

“Serving”+“Offset 5”<“threshold 4”, and

“Neighbour”>“R0”−“Offset 6”  Equation (5)

Here, “R0” is the radio quality in a cell having the best radio qualityamong cells using the same frequency as the frequency (f22 or f32) usedin a cell adjacent to the current camped cell of the mobile station UE(the “cell #22” or the “cell #32”).

In addition, the cell selector unit 16 may be configured to determinethat the predetermined condition B1 is satisfied, when the followingEquation (5-1) holds true, in addition to the Equation (5) describedabove holding true. Specifically, the Equation (5-1) holds true, whenthere is no cell that satisfies the predetermined radio quality amongthe cells using the same frequency as the frequency (f12 or f22) used inthe current camped cell (the “cell #12” or the “cell #22”) of the mobilestation UE.

“X”+“Offset 5”<“threshold 4”  Equation (5-1)

Here, “X” is the radio quality in each cell using the same frequency asthe frequency (f12 or f22) used in the current camped cell (the “cell#12” or the “cell #22”) of the mobile station UE.

For example, as FIG. 7 shows, when using the “cell #31” as the campedcell, and when a predetermined condition C1 is satisfied, the cellselector unit 16 is configured to change the camped cell from the “cell#31” to the “cell #32”.

Moreover, as FIG. 7 shows, when using the “cell #21” as the camped cell,and when the predetermined condition C1 is satisfied, the cell selectorunit 16 is configured to change the camped cell from the “cell #21” tothe “cell #11”.

Here, in a case where the “cell #11” or the “cell #21” is a macro cell,the cell selector unit 16 is configured to determine that thepredetermined condition C1 is satisfied, when the following Equation (6)holds true, namely, when the radio quality in the “cell #11” or the“cell #21” satisfies predetermined radio quality.

“Neighbour”+“Offset 7”>“threshold 5”  Equation (6)

Here, “Neighbour” is the radio quality in a cell adjacent to the currentcamped cell of the mobile station UE (the “cell #11” or the “cell #21”).

Meanwhile, in a case where the “cell #11” or the “cell #21” is a CSGcell, the cell selector unit 16 is configured to determine that thepredetermined condition C1 is satisfied, when the following Equation (7)is satisfied, namely, in addition to the condition of the Equation (6)described above being satisfied, when the difference between the radioquality in the “cell #11” or the “cell #21” and the best radio qualityamong the cells using any of the second frequencies f11 and f21 iswithin a predetermined offset.

“Neighbour”+“Offset 7”>“threshold 5”, and

“Neighbour”>“R0”−“Offset 8”  Equation (7)

Here, “R0” is the radio quality in a cell having the best radio qualityamong cells using the same frequency as the frequency (f11 or f21) usedin a cell adjacent to the current camped cell of the mobile station UE(the “cell #11” or the “cell #21”).

Note that the above-described operations of the mobile station UE, theradio base station eNB, the home base station HNB, and the switchingapparatus MME may be implemented by any of hardware, a software moduleexecuted by a processor, and a combination of both.

The software module may be provided in a storage medium of any form,such as a RAM (Random Access Memory), a flash memory, a ROM (Read OnlyMemory), an EPROM (Erasable Programmable ROM), an EEPROM (ElectronicallyErasable and Programmable ROM), a register, a hard disk, a removabledisk, or a CD-ROM.

Such a storage medium is connected to the processor so that theprocessor can read from and write into the storage medium. Moreover, thestorage medium may be integrated into the processor. Further, thestorage medium and the processor may be provided in an ASIC. The ASICmay be provided in the mobile station UE and the radio base station eNB.Furthermore, the storage medium and the processor may be provided in themobile station UE and the radio base station eNB as discrete components.

The present invention has been described in detail above using theembodiment above. It is apparent to those skilled in the art that thepresent invention is not limited to the embodiment described herein. Thepresent invention may be carried out as modified or corrected formswithout departing from the spirit and scope of the present inventiondefined by the appended claims. Therefore, the description of thepresent invention has been given for illustrative purposes only and isnot intended to limit the present invention whatsoever.

Note that the entire content of Japanese Patent Application No.2008-243401 (filed on Sep. 22, 2008) is incorporated herein byreference.

INDUSTRIAL APPLICABILITY

As described above, the present invention can provide a cell selectionmethod and a mobile station that allow a camped cell to be properlyselected in an environment where CSG cells and macro cells coexist.

1.-22. (canceled)
 23. A cell selection method in which a mobile stationselects a camped cell among a first cell using a first carrier frequencyand a second cell using a second carrier frequency which is differentfrom the first carrier frequency, the cell selection method comprisingsteps of: changing, at the mobile station, the camped cell from thefirst cell to the second cell, when the first cell is used as the campedcell, when a priority level of the second cell is the same as a prioritylevel of the first cell, and when a sum of radio quality in the secondcell and a predetermined offset is larger than a sum of radio quality inthe first cell and a predetermined parameter.
 24. A mobile stationconfigured to select a camped cell among a first cell using a firstcarrier frequency and a second cell using a second carrier frequencywhich is different from the first carrier frequency, the mobile stationcomprising: a cell selector unit configured to change the camped cellfrom the first general cell to the second specific cell, when the mobilestation uses the first cell as the camped cell, when a priority level ofthe second cell is the same as a priority level of the first cell, andwhen a sum of radio quality in the second cell and a predeterminedoffset is larger than a sum of radio quality in the first cell and apredetermined parameter.